How strong does a magnetic field have to be to affect the human body?

Asked by: Katrine Andrews, Gillingham

We are literally alive with electromagnetic fields, most obviously those generated by our nervous system. As such, we’re all potentially susceptible to magnetic fields, which create electric currents when they change or we move through them.

The intense fields used by medical scanners, which are around 100,000 times stronger than the Earth’s magnetic field, can trigger nausea, dizziness and a metallic taste in the mouth, but these effects are temporary.

The effects of more commonly encountered fields are, however, much less clear. Despite decades of claims about links between living in the magnetic fields generated by overhead powerlines and cancer, there’s no compelling evidence for long-term health effects.

That said, international guidelines for public exposure to magnetic fields set an upper limit of 40 millitesla – around 1,000 times stronger than the Earth’s magnetic field.

Read more:

• Do all planets have magnetic fields?
• Could a geomagnetic reversal kill us all?

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.